1. Field of the Invention
The present invention relates, generally, to control systems and methods for removing undesirable constituents from fluid streams. More specifically, the invention relates to a biological treatment system and method for cleansing and deodorizing gas effluents by reducing the concentration of odorous constituents present.
2. Description of Related Art
Increased industrialization and population growth in urban settings over the past several decades have presented important environmental concerns. Significant design problems are associated with the removal of unwanted odorous constituents from effluent gas streams when public health and aesthetic considerations make it desirable to do so.
Various techniques have been developed in response to the need for removal of odorous constituents from effluent gas streams. As a general rule, an effective technique should be tailored to the particular compound to be targeted. For example, in a sewage system environment, a primary cause of odor is hydrogen sulfide. This compound is detectable by the human olfactory sense at very low concentrations. In addition to the unpleasant odor associated with it, hydrogen sulfide is noted for its toxicity and its capacity for corroding materials with which it comes in contact.
Hydrogen sulfide is not the only undesirable constituent found in effluent gases. Others, such as amines, mercaptans and organic acids can be produced from a variety of sources. Because of the undesirability of introducing such constituents into the atmosphere, communities and governmental agencies may often formulate criteria for their regulation. A suitable odor control system, meeting such criteria, would substantially reduce the likelihood of any public nuisance or annoyance by removing, in a cost effective manner, substantial amounts of unwanted substances, preferably at or near the source of their production.
Removal of odorous constituents from a waste gas stream can be accomplished by several techniques. In the past, the treatment of polluted gases was performed mainly by means of chemical and physical processes. While chemical scrubbing, for example, is a well-established and reliable technique, it is associated with high operating and maintenance costs and involves the usage of hazardous chemicals.
In response to such drawbacks, biological treatment has emerged as an alternative technology for odor control and has demonstrated an ability to successfully treat high flows of contaminated gas with high inlet pollutant concentrations. In such systems, a biomass of pollutant-degrading microorganisms is cultivated on the surface of media packing in a scrubber column. The conversion of pollutants to innocuous compounds is mediated by the microorganisms as the contaminated air is passed through the biological scrubber column.
Biological scrubber columns have been disclosed. For example, in U.S. Pat. No. 5,445,660, Koers discloses an apparatus for cleaning gases with the aid of organic filtration material. Further, Bonnin et al., in U.S. Pat. No. 5,858,768, disclose a method for purifying and biodeodorizing gas effluents charged with pollutant matter.